In recent years, organic electronic structural elements, such as for example organic photodetectors, organic electrochromic devices and/or organic light-emitting diodes constructed on the basis of so-called “small molecules” were in particular improved by the fact that they contained n- and/or p-doped organic semiconductor layers which simplified the injection of the respective charge carriers, i.e. for example that the OLEDs achieved the same luminescence with a lower operating voltage. This technology is known, for example, from WO 2005086251 A2.
The doping of charge-injection layers is to a large extent unknown with solution-processed organic electronic structural elements such as for example polymeric OLEDs since it is difficult to separate several organic materials obtained from solution one on top of the other without detaching or partially dissolving the underlying layer/layers again.
In order to ensure good electron injection into the polymeric layers of organic electronic components, the cathode has multiple layers, for example, particularly advantageously made of barium and aluminum. Hereby, the barium is used as the electron source due to its lower work function.
The drawback of the technology is that barium is extremely susceptible to oxidation, i.e. it is instable, and aluminum cannot be used on its own as a cathode material since its injection barrier/work function is too high.
At the same time, the use of aluminum in the multilayer electrode with barium only provides primary oxidation protection with the coating of the oxidation-susceptible barium layer.